University of North Carolina at Chapel Hill Graduate School
Doi
Abstract
Silicate weathering is one of the driving forces of element cycling between atmosphere, hydrosphere, lithosphere, modulating habitats on Earth’s surface for the biosphere. Lithium (Li) and potassium (K) isotope ratios (expressed as δ7Li and δ41K) have potentials to trace weathering processes as the isotopes are highly fractionated by fluid-mineral interactions. This dissertation focuses on Li and K isotope fractionations during chemical weathering based on experiments and field observations and their links to element cycles. Chapter 2 develops an improved protocol for chromatographic isolation of Li, enabling reliable Li isotope analysis. Chapter 3 provides a novel view on Li isotope behavior during clay adsorption, following a Rayleigh-type model in a closed system. Chapter 4 investigates K isotope fractionation during clay adsorption. Combined with synchrotron radiation, I highlight opposite K isotope fractionations during clay adsorption and incorporation. Chapter 5 investigates Li and K isotope fractionations during silicate dissolution, thus providing supplementary knowledge of weathering-driven isotope fractionation. Chapter 6 assesses the Li isotope composition in Hawaiian regoliths forming on distinct climate zones and addresses comparative contributions of external additions, native sources, and biogeochemical cycles. Chapter 7 evaluates the K isotope composition in Hawaiian regoliths on distinct climate zones and highlight the use of K isotopes for climate tracing. Chapter 8 leverages the use of K isotope in soils and plants to trace biological K utilization. In sum, this dissertation emphasizes and explains similarity and difference between Li and K isotope fractionation during weathering.Doctor of Philosoph
